Background: The aim of this study was to investigate how behavioural states related to different levels of stress affected the increments of glomerular filtration rate induced by an acute protein load.
Methods: Thirteen healthy subjects were enrolled. Each subject was studied from 9:00 h to 15:00 h on two consecutive days. In random order, after a protein meal (1.2 g/kg b.w. of protein), each subject was required to remain in a relaxing, sitting position (resting period, R), or to solve graphical and mathematical problems (behavioural stress period, S). Mean blood pressure (MBP) and heart rate (HR) were monitored by an ambulatory blood pressure device. Urine samples collected in each period were used to measure glomerular filtration rate (GFR, creatinine clearance) and urinary sodium excretion (UNa+V).
Results: Significant decreases in MBP and HR were observed during the resting period after the protein load, which significantly increased GFR. There was also a large increase of UNa+V. During S, the GFR changes were no longer seen whereas the increse of UNa+V was maintained. HR and MBP did not change compared to the prestimulus period.
Conclusions: We conclude that in healthy subjects behavioural stress can blunt the increase in GFR that follows a protein load, presumably by neuro-humoral activated mechanisms. In our experimental conditions, behavioural stress did not affect UNa+V.